Evening light environments can be designed to consolidate and increase the duration of REM-sleep.

Evening exposure to short-wavelength light has disruptive effects on circadian rhythms and sleep. These effects can be mitigated by blocking short-wavelength (blue) frequencies, which has led to the development of evening blue-depleted light environments (BDLEs). We have previously reported that residing 5 days in an evening BDLE, compared with residing in a normal indoor light environment of similar photopic lux, advances circadian rhythms and increases the duration of rapid eye movement (REM) sleep in a randomized cross-over trial with twelve healthy participants. The current study extends these findings by testing whether residing in the evening BDLE affects the consolidation and microstructure of REM sleep in the same sample. Evening BDLE significantly reduces the fragmentation of REM sleep (p = 0.0003), and REM sleep microarousals in (p = 0.0493) without significantly changing REM density or the latency to first REM sleep episode. Moreover, the increased accumulation of REM sleep is not at the expense of NREM stage 3 sleep. BDLE further has a unique effect on REM sleep fragmentation (p = 0.0479) over and above that of circadian rhythms phase-shift, indicating a non-circadian effect of BDLE. If these effects can be replicated in clinical populations, this may have a therapeutic potential in disorders characterized by fragmented REM sleep.

Gene expression in the rat cerebral cortex: comparison of recovery sleep and hypnotic-induced sleep.

Most hypnotic medications currently on the market target some aspect of GABAergic neurotransmission. Although all such compounds increase sleep, these drugs differentially affect the activity of the cerebral cortex as measured by the electroencephalogram. Whereas benzodiazepine medications such as triazolam tend to suppress slow wave activity in the cortex, the GABA(B) ligand gamma-hydroxybutyrate greatly enhances slow wave activity and the non-benzodiazepine, zolpidem, which binds to the omega1 site on the GABA(A) receptor/Cl(-) ionophore complex, is intermediate in this regard. Our previous studies have demonstrated that a small number of genes exhibit increased expression in the cerebral cortex of the mouse and rat during recovery sleep after sleep deprivation: egr-3, fra-2, grp78, grp94, ngfi-b, and nr4a3. Using these genes as a panel of biomarkers associated with sleep, we asked whether hypnotic medications induce similar molecular changes in the rat cerebral cortex to those observed when both sleep continuity and slow wave activity are enhanced during recovery sleep. We find that, although each drug increases the expression of a subset of genes in the panel of biomarkers, no drug fully replicates the molecular changes in the cortex associated with recovery sleep. Furthermore, high levels of slow wave activity in the cortex are correlated with increased expression of fra-2 whereas the expression of grp94 is correlated with body temperature. These results demonstrate that sleep-related changes in gene expression may be affected by physiological covariates of sleep and wakefulness rather than by vigilance state per se.

Gene expression in the rat brain during sleep deprivation and recovery sleep: an Affymetrix GeneChip study.

Previous studies have demonstrated that macromolecular synthesis in the brain is modulated in association with the occurrence of sleep and wakefulness. Similarly, the spectral composition of electroencephalographic activity that occurs during sleep is dependent on the duration of prior wakefulness. Since this homeostatic relationship between wake and sleep is highly conserved across mammalian species, genes that are truly involved in the electroencephalographic response to sleep deprivation might be expected to be conserved across mammalian species. Therefore, in the rat cerebral cortex, we have studied the effects of sleep deprivation on the expression of immediate early gene and heat shock protein mRNAs previously shown to be upregulated in the mouse brain in sleep deprivation and in recovery sleep after sleep deprivation. We find that the molecular response to sleep deprivation and recovery sleep in the brain is highly conserved between these two mammalian species, at least in terms of expression of immediate early gene and heat shock protein family members. Using Affymetrix Neurobiology U34 GeneChips , we also screened the rat cerebral cortex, basal forebrain, and hypothalamus for other genes whose expression may be modulated by sleep deprivation or recovery sleep. We find that the response of the basal forebrain to sleep deprivation is more similar to that of the cerebral cortex than to the hypothalamus. Together, these results suggest that sleep-dependent changes in gene expression in the cerebral cortex are similar across rodent species and therefore may underlie sleep history-dependent changes in sleep electroencephalographic activity.

Dopaminergic-adrenergic interactions in the wake promoting mechanism of modafinil.

Adrenergic signaling regulates the timing of sleep states and sleep state-dependent changes in muscle tone. Recent studies indicate a possible role for noradrenergic transmission in the wake-promoting action of modafinil, a widely used agent for the treatment of excessive sleepiness. We now report that noradrenergic projections from the locus coeruleus to the forebrain are not necessary for the wake-promoting action of modafinil. The efficacy of modafinil was maintained after treatment of C57BL/6 mice with N-(2-chloroethyl)-N-ethyl 2-bromobenzylamine (DSP-4), which eliminates all noradrenaline transporter-bearing forebrain noradrenergic projections. However, the necessity for adrenergic receptors in the wake-promoting action of modafinil was demonstrated by the observation that the adrenergic antagonist terazosin suppressed the response to modafinil in DSP-4 treated mice. The wake-promoting efficacy of modafinil was also blunted by the dopamine autoreceptor agonist quinpirole. These findings implicate non-noradrenergic, dopamine-dependent adrenergic signaling in the wake-promoting mechanism of modafinil. The anatomical specificity of these dopaminergic-adrenergic interactions, which are present in forebrain areas that regulate sleep timing but not in brain stem areas that regulate sleep state-dependent changes in muscle tone, may explain why modafinil effectively treats excessive daytime sleepiness in narcolepsy but fails to prevent the loss of muscle tone that occurs in narcoleptic patients during cataplexy.

Sleep and circadian abnormalities in a transgenic mouse model of Alzheimer's disease: a role for cholinergic transmission.

The Tg2576 mouse model of Alzheimer's disease (AD) exhibits age-dependent amyloid beta (Abeta) deposition in the brain. We studied electroencephalographically defined sleep and the circadian regulation of waking activities in Tg2576 mice to determine whether these animals exhibit sleep abnormalities akin to those in AD. In Tg2576 mice at all ages studied, the circadian period of wheel running rhythms in constant darkness was significantly longer than that of wild type mice. In addition, the increase in electroencephalographic delta (1-4 Hz) power that occurs during non-rapid eye movement sleep after sleep deprivation was blunted in Tg2576 mice relative to controls at all ages studied. Electroencephalographic power during non-rapid eye movement sleep was shifted to higher frequencies in plaque-bearing mice relative to controls. The wake-promoting efficacy of the acetylcholinesterase inhibitor donepezil was lower in plaque-bearing Tg2576 mice than in controls. Sleep abnormalities in Tg2576 mice may be due in part to a cholinergic deficit in these mice. At 22 months of age, two additional deficits emerged in female Tg2576 mice: time of day-dependent modulation of sleep was blunted relative to controls and rapid eye movement sleep as a percentage of time was lower in Tg2576 than in wild type controls. The rapid eye movement sleep deficit in 22 month-old female Tg2576 mice was abolished by brief passive immunization with an N-terminal antibody to Abeta. The Tg2576 model provides a uniquely powerful tool for studies on the pathophysiology of and treatments for sleep deficits and associated cholinergic abnormalities in AD.

Altered rapid eye movement sleep timing in serotonin transporter knockout mice.

The monoamine neurotransmitter serotonin has long been implicated in development and maintenance of sleep patterns, yet the role of the serotonin transporter (SERT) in these processes has not been evaluated in detail. We report that genetically engineered SERT knockout mice exhibit more REM sleep (REMS) than wild type littermates (11 vs 7% of recording time under baseline conditions) and display more frequent REMS bouts that last longer. This phenotype resembles the previously reported long-term effect of repeated treatment with SERT inhibitor compounds rather than the acute REMS suppressing effect of treatment with such compounds, and is thus likely to reflect neuroadaptations to the absence of SERT, rather than an acute effect of its absence in the adult. While electroencephalographic (EEG) spectra did not differ between SERT knockout and wild type mice during non-REM sleep (NREMS) or REMS, the dynamics of the EEG during the transition from NREMS to REMS differed between the genotypes. The surge in EEG power in both the 6-9 Hz and 10-16 Hz ranges that occurs just prior to the onset of REMS (pre-REMS power surge) is of greater magnitude in SERT knockout mice than in wild type littermate controls. This observation contrasts with the reduced magnitude pre-REMS power surge observed in rats subjected to REMS deprivation relative to yoked controls. These results indicate that the pre-REMS power surge is influenced by REMS history and by monoaminergic transmission. Genetic differences in serotonin systems and developmental exposure to SERT blockers are likely to exert effects on REMS.

Disorders of the circadian clock: etiology and possible therapeutic targets.

The mammalian circadian clock in the suprachiasmatic nuclei (SCN) of the hypothalamus conveys 24-hr rhythmicity to sleep-wake cycles, temperature, locomotor activity and virtually all other behavioral and physiological processes. In order for these cycles to be adaptive, they must be synchronized, or entrained, to the 24-hr light/dark cycle produced by the rotation of the Earth. The timing of circadian variables relative to the light/dark cycle, i.e., the phase angle of entrainment, is influenced by intrinsic circadian clock properties that are to an extent genetically determined, and thus varies between individuals. In extreme cases (advanced or delayed sleep phase syndrome) or during shift work or jet lag, the phase angle of entrainment may be incompatible with work requirements or other social demands, resulting in negative consequences to health and productivity. This review describes the etiology of circadian disorders within the context of formal circadian clock properties and summarizes studies in humans and in other species which link specific genetic loci to circadian clock function and malfunction. The proteins encoded by these genetic loci play key roles in the intracellular feedback loop that generates circadian rhythms, and thus represent therapeutic targets for the treatment of both endogenous and exogenous circadian disorders.

Dopaminergic role in stimulant-induced wakefulness.

The role of dopamine in sleep regulation and in mediating the effects of wake-promoting therapeutics is controversial. In this study, polygraphic recordings and caudate microdialysate dopamine measurements in narcoleptic dogs revealed that the wake-promoting antinarcoleptic compounds modafinil and amphetamine increase extracellular dopamine in a hypocretin receptor 2-independent manner. In mice, deletion of the dopamine transporter (DAT) gene reduced non-rapid eye movement sleep time and increased wakefulness consolidation independently from locomotor effects. DAT knock-out mice were also unresponsive to the normally robust wake-promoting action of modafinil, methamphetamine, and the selective DAT blocker GBR12909 but were hypersensitive to the wake-promoting effects of caffeine. Thus, dopamine transporters play an important role in sleep regulation and are necessary for the specific wake-promoting action of amphetamines and modafinil.

Targeted deletion of the Vgf gene indicates that the encoded secretory peptide precursor plays a novel role in the regulation of energy balance.

To determine the function of VGF, a secreted polypeptide that is synthesized by neurons, is abundant in the hypothalamus, and is regulated in the brain by electrical activity, injury, and the circadian clock, we generated knockout mice lacking Vgf. Homozygous mutants are small, hypermetabolic, hyperactive, and infertile, with markedly reduced leptin levels and fat stores and altered hypothalamic proopiomelanocortin (POMC), neuropeptide Y (NPY), and agouti-related peptide (AGRP) expression. Furthermore, VGF mRNA synthesis is induced in the hypothalamic arcuate nuclei of fasted normal mice. VGF therefore plays a critical role in the regulation of energy homeostasis, suggesting that the study of lean VGF mutant mice may provide insight into wasting disorders and, moreover, that pharmacological antagonism of VGF action(s) might constitute the basis for treatment of obesity.

Circadian behavior and plasticity of light-induced c-fos expression in SCN of tau mutant hamsters.

In hamsters homozygous for the circadian clock mutation tau, the photic history dramatically affects the magnitude of light-induced circadian phase shifts. The maximum amplitude of phase shifts produced by 1-h light pulses presented at CT 14 was less than 2 h in animals that had been in DD for 2 days, whereas animals that had been kept in DD for 49 days could be shifted by more than 8 h. In this study, the authors compared the effect of previous light history on the amplitude of circadian phase shifts and on c-fos expression in the SCN of tau mutant hamsters. Although the maximum amplitude of behavioral phase shifts was drastically different between animals that had been held for either 2 or 49 days in DD, maximal fos induction was not significantly different in these two groups. However, photic thresholds for light-induced behavioral phase shifts, c-fos mRNA, and Fos immunoreactivity were closely correlated within both groups, and these thresholds were lower (more sensitive to light) after 49 than after 2 days in DD. The correlation between phase shifting and Fos induction thresholds, under conditions where both responses are dramatically altered by the previous light history, demonstrates an association between changes in circadian behavioral phase-shifting responses of tau mutant hamsters and plasticity of light-induced c-fos expression in SCN. However, because the maximum amplitudes of Fos induction and phase shifting were not correlated in animals that had been in DD for 2 days, we speculate that the level of c-fos expression does not directly determine phase shift amplitude.

Regulation of the vgf gene in the golden hamster suprachiasmatic nucleus by light and by the circadian clock.

By using in situ hybridization in the golden hamster brain, we have found that vgf mRNA levels are induced as a response to light stimulation in the suprachiasmatic nuclei (SCN), the site of the mammalian circadian pacemaker. The induction exhibits delayed kinetics relative to known light-induced immediate early genes: induction of vgf mRNA occurs over a period of 3 to 9 hours after light exposure. Photic induction of vgf expression does not occur in the paraventricular nucleus (PVN) of the hypothalamus, though this nucleus expresses vgf at the mRNA and protein levels. Photic induction of vgf in the SCN occurs only at circadian times when light also causes a phase shift of the circadian system. The irradiance threshold of vgf induction in the SCN closely matches that of the behavioral phase shifting response. In addition, basal expression of vgf in the SCN, but not in the PVN, exhibits a circadian rhythm in constant darkness. The photic induction and circadian rhythm of vgf expression are anatomically separated in the caudal and rostral portions of the SCN, respectively. These results represent the first example of a delayed response to light relative to light-induced immediate early genes at the mRNA level in the SCN.